Multiple collections of user-defined metadata for self-describing objects

ABSTRACT

Exemplary embodiments provide the ability to associate multiple collections of metadata to objects. In one embodiment, a storage system comprises: a processor; a memory; at least one object, each object including content data; system metadata associated with each object; and a plurality of named collections of user-defined metadata associated with each object. Each named collection of the plurality of named collections is separately addressable by a request. In some embodiments, at least one named collection of user-defined metadata of one object of the at least one object includes an access control list, and the access control list of a named collection specifies permissible access to the named collection. The one object has an object-level access control list which specifies permissible access to the one object and which is different from the access control list for the named collection associated with the one object.

BACKGROUND OF THE INVENTION

The present invention relates generally to storage systems and, moreparticularly, to system and method for providing multiple collections ofuser-defined metadata for objects in storage system such as a replicatedobject storage system.

Most object storage systems have the ability to associate metadata (dataabout data) to objects ingested in the system. This metadata is utilizedto annotate the objects by providing more descriptive information aboutthe object. The additional metadata will provide the needed informationto help the consumer identify objects with similar criteria foractivities such as analytics and discovery, thereby creatingself-describing objects. As objects become more self-describing, thisallows for usage of the objects for many different purposes andconsumers that may desire to provide additional metadata.

Current methods to associate metadata with objects consist of formingthe information into well-defined formats such as XML or JSON andassociating it to the object as a single entity. In order for multipleconsumers to utilize and augment the metadata, there must becoordination with all producers and consumers as to the format of themetadata; this ensures no incompatibilities are created or othermetadata is destroyed. The coordination of changes between multipleconsumers/producers can be difficult to accomplish as the number ofconsumers/producers grows, as those consumers/producers could be fromseparate and competing companies/products.

Without a standard or capability for separation, different applicationsMUST still be aware that tags/headers could exist that have the samename, but generated by another software entity.

BRIEF SUMMARY OF THE INVENTION

Exemplary embodiments of the invention provide the ability to associatemultiple collections of metadata to objects. Each collection of metadatamay provide a purposeful meaning called an annotation. A name isassociated with these annotations allowing for multiple annotations perobject. These annotations are named collections of user-defined orcustom metadata for self-describing objects.

An object together with its annotations provides for creatingself-describing objects within an object storage system. Eachself-describing object contains enough information about itself to allowfor utilization of the object without having to collect informationabout the object from other sources such as relational databases. Thiswill enable the ability to construct systems and methods that canoperate on the ever increasing volume of objects by only interactingwith the object storage system.

A given consumer/producer can create its own named annotation(s) andformat the content of the annotation into a form that is suitable totheir needs (e.g., XML, JSON, comma-separated, etc.) without having tobe concerned about the existence or non-existence of otherconsumer/producers. Nor is it required to have a standard layout/schemadefined for the overall metadata. This will allow for multiple uses ofthe same data. For example, a digital image can be annotated with a widevariety of information by different software without the need to knowthat other software is using the image. The different annotations cancontain information such as face recognition, cloud coverage, weatherpattern, object identification, relationship to other images, and manyother topics. With named annotations, the result will provide for easymodification of individual annotations without having to rewrite allannotations, provide for the ability to implement security for eachannotation, and identify all objects that contain a certain kind ofinformation using the name as search criteria. Furthermore, accesssecurity can be applied to the whole object as well as each individualannotation. With this level of security, it will be possible to providedifferent access control to construct different views of the same objectbased on the credentials of the requesting consumer.

In general, object storage systems have the concept of attachingmetadata to objects. Each may have different ways of naming orstructuring individual elements to provide an implied organization.Embodiments of this invention provide individual collections of metadataor annotations that allow for differing layout/formats for the metadataalong with restricting access to these collections via Access ControlList (ACL) constructs.

In accordance with an aspect of the present invention, a storage systemcomprises: a processor; a memory; at least one object, each objectincluding content data; system metadata associated with each object; anda plurality of named collections of user-defined metadata associatedwith each object. Each named collection of the plurality of namedcollections is separately addressable by a request.

In some embodiments, at least one named collection of user-definedmetadata of one object of the at least one object includes an accesscontrol list, and the access control list of a named collectionspecifies permissible access to the named collection. The one object hasan object-level access control list which specifies permissible accessto the one object and which is different from the access control listfor the named collection associated with the one object. The storagesystem further comprises an unnamed collection of user-defined metadatawhich is addressable by a request.

In specific embodiments, the request is one of: a PUT request to createor replace a named collection of user-defined metadata; a GET request toretrieve a named collection of user-defined metadata; a HEAD request toretrieve details of a named collection of user-defined metadata; a POSTrequest to update a named collection of user-defined metadata; a DELETErequest to delete a named collection of user-defined metadata; a WholeI/O (Input/Output) PUT request to create or replace the content data ofthe one object and a named collection of user-defined metadataassociated with the one object; or a Whole I/O GET request to retrievethe content data of the one object and a named collection ofuser-defined metadata associated with the one object.

Another aspect of the invention is directed to a storage system having aplurality of nodes, the nodes being grouped into a plurality of clustersystems each having multiple nodes. System metadata of objects arestored in a form of metadata objects in a set of regions distributedacross the storage system. The objects include content data. A method ofproviding user-defined metadata for one object of the objects comprises,for the one object: providing a plurality of named collections ofuser-defined metadata; and associating the plurality of namedcollections of user-defined metadata with the one object. Each namedcollection of the plurality of named collections is separatelyaddressable by a request.

In some embodiments, the method further comprises providing an unnamedcollection of user-defined metadata which is addressable by a requestand associating the unnamed collection of user-defined metadata with theone object.

Another aspect of this invention is directed to a storage system havinga plurality of nodes, the nodes being grouped into a plurality ofcluster systems each having multiple nodes. System metadata of objectsare stored in a form of metadata objects in a set of regions distributedacross the array. The objects include content data. An apparatus forproviding user-defined metadata for one object of the objects comprisesa controller and a memory. The controller is operable, for the oneobject, to: provide a plurality of named collections of user-definedmetadata; and associate the plurality of named collections ofuser-defined metadata with the one object. Each named collection of theplurality of named collections is separately addressable by a request.

In some embodiments, the controller is operable to provide an accesscontrol list for at least one named collection of user-defined metadataof the one object. The access control list of a named collectionspecifies permissible access to the named collection. The controller isoperable to provide an object-level access control list for the oneobject which specifies permissible access to the one object and which isdifferent from the access control list for the named collectionassociated with the one object. The controller is operable to provide anunnamed collection of user-defined metadata which is addressable by arequest and associate the unnamed collection of user-defined metadatawith the one object.

These and other features and advantages of the present invention willbecome apparent to those of ordinary skill in the art in view of thefollowing detailed description of the specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a fixed content storage archivein which the method and apparatus of the invention may be applied.

FIG. 2 is a simplified representation of a redundant array ofindependent nodes each of which is symmetric and supports an archivecluster application.

FIG. 3 is a high level representation of the various components of thearchive cluster application executing on a given node.

FIG. 4 illustrates an example of the components of the metadatamanagement system on a given node of the cluster.

FIG. 5 shows an example of the core construction of an object.

FIG. 6 shows an example of an object having system of metadata andmultiple named collections of user-defined metadata herein referred toas annotations.

FIG. 7 shows an example of an object having a plurality of annotationsand access control lists (ACLs).

FIG. 8 shows an example of an apparatus for implementing the use ofmultiple annotations for an object.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the invention, reference ismade to the accompanying drawings which form a part of the disclosure,and in which are shown by way of illustration, and not of limitation,exemplary embodiments by which the invention may be practiced. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. Further, it should be noted that while thedetailed description provides various exemplary embodiments, asdescribed below and as illustrated in the drawings, the presentinvention is not limited to the embodiments described and illustratedherein, but can extend to other embodiments, as would be known or aswould become known to those skilled in the art. Reference in thespecification to “one embodiment,” “this embodiment,” or “theseembodiments” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention, and the appearances ofthese phrases in various places in the specification are not necessarilyall referring to the same embodiment. Additionally, in the followingdetailed description, numerous specific details are set forth in orderto provide a thorough understanding of the present invention. However,it will be apparent to one of ordinary skill in the art that thesespecific details may not all be needed to practice the presentinvention. In other circumstances, well-known structures, materials,circuits, processes and interfaces have not been described in detail,and/or may be illustrated in block diagram form, so as to notunnecessarily obscure the present invention.

Furthermore, some portions of the detailed description that follow arepresented in terms of algorithms and symbolic representations ofoperations within a computer. These algorithmic descriptions andsymbolic representations are the means used by those skilled in the dataprocessing arts to most effectively convey the essence of theirinnovations to others skilled in the art. An algorithm is a series ofdefined steps leading to a desired end state or result. In the presentinvention, the steps carried out require physical manipulations oftangible quantities for achieving a tangible result. Usually, though notnecessarily, these quantities take the form of electrical or magneticsignals or instructions capable of being stored, transferred, combined,compared, and otherwise manipulated. It has proven convenient at times,principally for reasons of common usage, to refer to these signals asbits, values, elements, symbols, characters, terms, numbers,instructions, or the like. It should be borne in mind, however, that allof these and similar terms are to be associated with the appropriatephysical quantities and are merely convenient labels applied to thesequantities. Unless specifically stated otherwise, as apparent from thefollowing discussion, it is appreciated that throughout the description,discussions utilizing terms such as “processing,” “computing,”“calculating,” “determining,” “displaying,” or the like, can include theactions and processes of a computer system or other informationprocessing device that manipulates and transforms data represented asphysical (electronic) quantities within the computer system's registersand memories into other data similarly represented as physicalquantities within the computer system's memories or registers or otherinformation storage, transmission or display devices.

The present invention also relates to an apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may include one or more general-purposecomputers selectively activated or reconfigured by one or more computerprograms. Such computer programs may be stored in a computer-readablestorage medium including non-transient medium, such as, but not limitedto optical disks, magnetic disks, read-only memories, random accessmemories, solid state devices and drives, or any other types of mediasuitable for storing electronic information. The algorithms and displayspresented herein are not inherently related to any particular computeror other apparatus. Various general-purpose systems may be used withprograms and modules in accordance with the teachings herein, or it mayprove convenient to construct a more specialized apparatus to performdesired method steps. In addition, the present invention is notdescribed with reference to any particular programming language. It willbe appreciated that a variety of programming languages may be used toimplement the teachings of the invention as described herein. Theinstructions of the programming language(s) may be executed by one ormore processing devices, e.g., central processing units (CPUs),processors, or controllers.

Exemplary embodiments of the invention, as will be described in greaterdetail below, provide apparatuses, methods and computer programs forassociating multiple named collections of user-defined metadata toobjects.

I. Fixed Content Distributed Data Storage

A need has developed for the archival storage of “fixed content” in ahighly available, reliable and persistent manner that replaces orsupplements traditional tape and optical storage solutions. The term“fixed content” typically refers to any type of digital information thatis expected to be retained without change for reference or otherpurposes. Examples of such fixed content include, among many others,e-mail, documents, diagnostic images, check images, voice recordings,film and video, and the like. The traditional Redundant Array ofIndependent Nodes (RAIN) storage approach has emerged as thearchitecture of choice for creating large online archives for thestorage of such fixed content information assets. By allowing nodes tojoin and exit from a cluster as needed, RAIN architectures insulate astorage cluster from the failure of one or more nodes. By replicatingdata on multiple nodes, RAIN-type archives can automatically compensatefor node failure or removal. Typically, RAIN systems are largelydelivered as hardware appliances designed from identical componentswithin a closed system.

FIG. 1 illustrates one such scalable disk-based archival storagemanagement system. The nodes may comprise different hardware and thusmay be considered “heterogeneous.” A node typically has access to one ormore storage disks, which may be actual physical storage disks, orvirtual storage disks, as in a storage area network (SAN). The archivecluster application (and, optionally, the underlying operating system onwhich that application executes) that is supported on each node may bethe same or substantially the same. The software stack (which mayinclude the operating system) on each node is symmetric, whereas thehardware may be heterogeneous. Using the system, as illustrated in FIG.1, enterprises can create permanent storage for many different types offixed content information such as documents, e-mail, satellite images,diagnostic images, check images, voice recordings, video, and the like,among others. These types are merely illustrative, of course. Highlevels of reliability are achieved by replicating data on independentservers, or so-called storage nodes. Preferably, each node is symmetricwith its peers. Thus, because preferably any given node can perform allfunctions, the failure of any one node has little impact on thearchive's availability.

As described in commonly owned U.S. Pat. No. 7,155,466, it is known in aRAIN-based archival system to incorporate a distributed softwareapplication executed on each node that captures, preserves, manages, andretrieves digital assets. FIG. 2 illustrates one such system. A physicalboundary of an individual archive is referred to as a cluster (or asystem). Typically, a cluster is not a single device, but rather acollection of devices. Devices may be homogeneous or heterogeneous. Atypical device is a computer or machine running an operating system suchas Linux. Clusters of Linux-based systems hosted on commodity hardwareprovide an archive that can be scaled from a few storage node servers tomany nodes that store thousands of terabytes of data. This architectureensures that storage capacity can always keep pace with anorganization's increasing archive requirements.

In storage systems such as described above, data typically isdistributed across the cluster randomly so that the archive is alwaysprotected from device failure. If a disk or node fails, the clusterautomatically fails over to other nodes in the cluster that maintainreplicas of the same data. While this approach works well from a dataprotection standpoint, a calculated mean time to data loss (MTDL) forthe cluster may not be as high as desired. In particular, MTDL typicallyrepresents a calculated amount of time before the archive will losedata. In a digital archive, any data loss is undesirable, but due to thenature of hardware and software components, there is always apossibility (however remote) of such an occurrence. Because of therandom distribution of objects and their copies within an archivecluster, MTDL may end up being lower than required since, for example, aneeded copy of an object may be unavailable if a given disk (on which amirror copy is stored) within a given node fails unexpectedly.

As shown in FIG. 2, an illustrative cluster in which the presentinvention is implemented preferably comprises the following generalcategories of components: nodes 202, a pair of network switches 204,power distribution units (PDUs) 206, and uninterruptible power supplies(UPSs) 208. A node 202 typically comprises one or more commodity serversand contains a CPU (e.g., CPU, suitable random access memory (RAM), oneor more hard drives (e.g., standard IDE/SATA, SCSI, or the like), andtwo or more network interface (NIC) cards. A typical node is a 2U rackmounted unit with a 2.4 GHz chip, 512 MB RAM, and six (6) 200 GB harddrives. This is not a limitation, however. The network switches 204typically comprise an internal switch 205 that enables peer-to-peercommunication between nodes, and an external switch 207 that allowsextra-cluster access to each node. Each switch requires enough ports tohandle all potential nodes in a cluster. Ethernet or GigE switches maybe used for this purpose. PDUs 206 are used to power all nodes andswitches, and the UPSs 208 are used that protect all nodes and switches.Although not meant to be limiting, typically a cluster is connectable toa network, such as the public Internet, an enterprise intranet, or otherwide area or local area network. In an illustrative embodiment, thecluster is implemented within an enterprise environment. It may bereached, for example, by navigating through a site's corporate domainname system (DNS) name server. Thus, for example, the clusters domainmay be a new sub-domain of an existing domain. In a representativeimplementation, the sub-domain is delegated in the corporate DNS serverto the name servers in the cluster itself. End users access the clusterusing any conventional interface or access tool. Thus, for example,access to the cluster may be carried out over any IP-based protocol(HTTP, FTP, NFS, AFS, SMB, a Web service, or the like), via an API(Application Program Interface), or through any other known orlater-developed access method, service, program, or tool.

Client applications access the cluster through one or more types ofexternal gateways such as standard UNIX file protocols, or HTTP APIs.The archive preferably is exposed through a virtual file system that canoptionally sit under any standard UNIX file protocol-oriented facility.These include NFS, FTP, SMB/CIFS, or the like.

In one embodiment, the archive cluster application runs on a redundantarray of independent nodes (H-RAIN) that are networked together (e.g.,via Ethernet) as a cluster. The hardware of given nodes may beheterogeneous. For maximum reliability, however, preferably each noderuns an instance 300 of the distributed application (which may be thesame instance, or substantially the same instance), which comprisesseveral runtime components as now illustrated in FIG. 3. Thus, whilehardware may be heterogeneous, the software stack on the nodes (at leastas it relates to the present invention) is the same. These softwarecomponents comprise a gateway protocol layer 302, an access layer 304, afile transaction and administration layer 306, and a core componentslayer 308. The “layer” designation is provided for explanatory purposes,as one of ordinary skill will appreciate that the functions may becharacterized in other meaningful ways. One or more of the layers (orthe components therein) may be integrated or otherwise. Some componentsmay be shared across layers.

The gateway protocols in the gateway protocol layer 302 providetransparency to existing applications. In particular, the gatewaysprovide native file services such as NFS 310 and SMB/CIFS 312, as wellas a Web services API to build custom applications. HTTP support 314 isalso provided. The access layer 304 provides access to the archive. Inparticular, according to the invention, a Fixed Content File System(FCFS) 316 emulates a native file system to provide full access toarchive objects. FCFS gives applications direct access to the archivecontents as if they were ordinary files. Preferably, archived content isrendered in its original format, while metadata is exposed as files.FCFS 316 provides conventional views of directories and permissions androutine file-level calls, so that administrators can provisionfixed-content data in a way that is familiar to them. File access callspreferably are intercepted by a user-space daemon and routed to theappropriate core component (in layer 308), which dynamically creates theappropriate view to the calling application. FCFS calls preferably areconstrained by archive policies to facilitate autonomous archivemanagement. Thus, in one example, an administrator or application cannotdelete an archive object whose retention period (a given policy) isstill in force.

The access layer 304 preferably also includes a Web user interface (UI)318 and an SNMP gateway 320. The Web user interface 318 preferably isimplemented as an administrator console that provides interactive accessto an administration engine 322 in the file transaction andadministration layer 306. The administrative console 318 preferably is apassword-protected, Web-based GUI that provides a dynamic view of thearchive, including archive objects and individual nodes. The SNMPgateway 320 offers storage management applications easy access to theadministration engine 322, enabling them to securely monitor and controlcluster activity. The administration engine monitors cluster activity,including system and policy events. The file transaction andadministration layer 306 also includes a request manager process 324.The request manager 324 orchestrates all requests from the externalworld (through the access layer 304), as well as internal requests froma policy manager 326 in the core components layer 308.

In addition to the policy manager 326, the core components also includea metadata manager 328, and one or more instances of a storage manager330. A metadata manager 328 preferably is installed on each node.Collectively, the metadata managers in a cluster act as a distributeddatabase, managing all archive objects. On a given node, the metadatamanager 328 manages a subset of archive objects, where preferably eachobject maps between an external file (“EF,” the data that entered thearchive for storage) and a set of internal files (each an “IF”) wherethe archive data is physically located. The same metadata manager 328also manages a set of archive objects replicated from other nodes. Thus,the current state of every external file is always available to multiplemetadata managers on several nodes. In the event of node failure, themetadata managers on other nodes continue to provide access to the datapreviously managed by the failed node. The storage manager 330 providesa file system layer available to all other components in the distributedapplication. Preferably, it stores the data objects in a node's localfile system. Each drive in a given node preferably has its own storagemanager. This allows the node to remove individual drives and tooptimize throughput. The storage manager 330 also provides systeminformation, integrity checks on the data, and the ability to traversedirectly local structures.

As also illustrated in FIG. 3, the cluster manages internal and externalcommunication through a communications middleware layer 332 and a DNSmanager 334. The infrastructure 332 is an efficient and reliablemessage-based middleware layer that enables communication among archivecomponents. In an illustrated embodiment, the layer supports multicastand point-to-point communications. The DNS manager 334 runs distributedname services that connect all nodes to the enterprise server.Preferably, the DNS manager (either alone or in conjunction with a DNSservice) load balances requests across all nodes to ensure maximumcluster throughput and availability.

In an illustrated embodiment, an application instance executes on a baseoperating system 336, such as Linux, or the like. The communicationsmiddleware is any convenient distributed communication mechanism. Othercomponents may include FUSE (Filesystem in USErspace), which may be usedfor the Fixed Content File System (FCFS) 316. The NFS gateway 310 may beimplemented by a standard nfsd Linux Kernel NFS driver. The database ineach node may be implemented, which is an object-relational databasemanagement system (ORDBMS). The node may include a Web server, such asJetty, which is a Java HTTP server and servlet container. Of course, theabove mechanisms are merely illustrative.

The storage manager 330 on a given node is responsible for managing thephysical storage devices. Preferably, each storage manager instance isresponsible for a single root directory into which all files are placedaccording to its placement algorithm. Multiple storage manager instancescan be running on a node at the same time, and each usually represents adifferent physical disk in the system. The storage manager abstracts thedrive and interface technology being used from the rest of the system.When the storage manager instance is asked to write a file, it generatesa full path and file name for the representation for which it will beresponsible. In a representative embodiment, each object to be stored ona storage manager is received as raw data to be stored, with the storagemanager then adding its own metadata to the file as it stores the datato keep track of different types of information. By way of example, thismetadata includes: EF length (length of external file in bytes), IFSegment size (size of this piece of the Internal File), EF Protectionrepresentation (EF protection mode), IF protection role (representationof this internal file), EF Creation timestamp (external file timestamp),Signature (signature of the internal file at the time of the write(PUT), including a signature type), and EF Filename (external filefilename). Storing this additional metadata with the internal file dataprovides for additional levels of protection. In particular, scavengingcan create external file records in the database from the metadatastored in the internal files. Other policies can validate internal filehash against the internal file to validate that the internal fileremains intact.

Internal files may be “chunks” of data representing a portion of theoriginal “file” in the archive object, and they may be placed ondifferent nodes to achieve striping and protection blocks. This breakingapart of an external file into smaller chunked units is not arequirement, however; in the alternative, internal files may be completecopies of the external file. Typically, one external file entry ispresent in a metadata manager for each archive object, while there maybe many internal file entries for each external file entry. Typically,internal file layout depends on the system. In a given implementation,the actual physical format of this data on disk is stored in a series ofvariable length records.

The request manager 324 is responsible for executing the set ofoperations needed to perform archive actions by interacting with othercomponents within the system. The request manager supports manysimultaneous actions of different types, is able to roll-back any failedtransactions, and supports transactions that can take a long time toexecute. The request manager further ensures that read/write operationsin the archive are handled properly and guarantees all requests are in aknown state at all times. It also provides transaction control forcoordinating multiple read/write operations across nodes to satisfy agiven client request. In addition, the request manager caches metadatamanager entries for recently used files and provides buffering forsessions as well as data blocks.

A cluster's primary responsibility is to store an unlimited number offiles on disk reliably. A given node may be thought of as being“unreliable,” in the sense that it may be unreachable or otherwiseunavailable for any reason. A collection of such potentially unreliablenodes collaborate to create reliable and highly available storage.Generally, there are two types of information that need to be stored:the files themselves and the metadata about the files. Additionaldetails of the fixed content distributed data storage can be found inU.S. Patent Publication No. 2007/0189153 and U.S. Pat. No. 7,657,581,which are incorporated herein by reference.

II. Metadata Management

A metadata management system is responsible for organizing and providingaccess to given metadata, such as system metadata. This system metadataincludes information on files placed in the archive, as well asconfiguration information, information displayed on the administrativeUI, metrics, information on irreparable policy violations, and the like.Although not illustrated in detail, other types of metadata (e.g., usermetadata associated with archived files) may also be managed using themetadata management system that is now described.

In a representative embodiment of the cluster, the metadata managementsystem provides persistence for a set of metadata objects, which mayinclude one or more of the following object types (which are merelyillustrative):

ExternalFile: a file as perceived by a user of the archive;

Internal File: a file stored by the Storage Manager; typically, theremay be a one-to-many relationship between External Files and InternalFiles.

ConfigObject: a name/value pair used to configure the cluster;

AdminLogEntry: a message to be displayed on the administrator UI;

MetricsObject: a timestamped key/value pair, representing somemeasurement of the archive (e.g., number of files) at a point in time;and

PolicyState: a violation of some policy.

Each metadata object may have a unique name that preferably neverchanges. Metadata objects are organized into regions. A region comprisesan authoritative region copy and a “tolerable points of failure” (TPOF)number (a set of zero or more) backup region copies. With zero copies,the metadata management system is scalable but may not be highlyavailable. A region is selected by hashing one or more object attributes(e.g., the object's name, such as a fully qualified pathname, or portionthereof) and extracting a given number of bits of the hash value. Thesebits comprise a region number. The bits selected may be low order bits,high order bits, middle order bits, or any combination of individualbits. In a representative embodiment, the given bits are the low orderbits of the hash value. The object's attribute or attributes may behashed using any convenient hash function. These include, withoutlimitation, a Java-based hash function such asjava.lang.string.hashCode, and the like. Preferably, the number of bitscomprising the region number is controlled by a configuration parameter,referred to herein as regionMapLevel. If this configuration parameter isset to 6, for example, this results in 2⁶=64 regions. Of course, alarger number of regions are permitted, and the number of regions may beadjusted automatically using a namespace partitioning scheme.

Each region may be stored redundantly. As noted above, there is oneauthoritative copy of the region, and zero or more backup copies. Thenumber of backup copies is controlled by the metadata TPOF configurationparameter, as has been described. Preferably, region copies aredistributed across all the nodes of the cluster so as to balance thenumber of authoritative region copies per node, and to balance thenumber of total region copies per node.

The metadata management system stores metadata objects in a databaserunning on each node. This database is used to support the region map.Preferably, there is a schema for each region copy, and in each schemathere is a table for each type of metadata object. A schema is simply anamespace that can own tables, indexes, procedures, and other databaseobjects. Each region preferably has its own schema. Each schema has acomplete set of tables, one for each metadata object. A row in one ofthese tables corresponds to a single metadata object.

As used herein, a namespace is a logical partition of the cluster, andessentially serves as a collection of objects particular to at least onedefined application. Each namespace has a private filesystem withrespect to other namespaces. Moreover, access to one namespace does notgrant a user access to another namespace. A cluster/system of nodes is aphysical archive instance.

As illustrated in FIG. 4, each node 400 has a set of processes orcomponents: one or more region managers (RGM) 402 a-n, a metadatamanager (MM) 404, at least one metadata manager client (MMC) 406, and adatabase 408 having one or more schemas 410 a-n. The RGM(s), MM and MMCcomponents execute with a virtual machine 412, such as a Java virtualmachine. There is one RGM for each region copy. Thus, there is an RGMfor the authoritative region copy, an RGM for each backup region copy,and an RGM for each incomplete region copy. There is also a databaseschema 410 for each RGM 402, which manages that schema. The databasealso stores the region map 405. Each node preferably has the same globalview of the region map, with requirement being enforced by asynchronization scheme. A region manager RGM 402 is responsible foroperating on a region copy (be it authoritative, backup or incomplete,as the case may be), and for executing requests submitted by themetadata manager clients 406 and by other region managers 402. Requestsare provided to a given RGM through any convenient means, such as thecommunications middleware or other messaging layer illustrated in FIG.3. The region manager provides an execution environment in which theserequests execute, e.g., by providing a connection to the database,configured to operate on the schema that is being managed by that RGM.Each region manager stores its data in the database 408. The metadatamanager 404 is a top-level component responsible for metadata managementon the node. It is responsible for creating and destroying regionmanagers (RGMs) and organizing resources needed by the RGMs, e.g.,cluster configuration information and a pool of database connections.Preferably, a given metadata manager (in a given node) acts as a leaderand is responsible for determining which metadata managers (across a setor subset of nodes) are responsible for which region copies. A leaderelection algorithm, such as the bully algorithm, or a variant thereof,may be used to select the metadata manager leader. Preferably, each nodehas a single metadata manager, although it is possible to run multipleMMs per node. Once region ownership has been established by thenamespace partitioning scheme (as will be described below), eachmetadata manager is responsible for adjusting its set of one or moreregion managers accordingly. System components (e.g., the administrativeengine, the policy manager, and the like) interact with the metadatamanager MM through the metadata manager client. The MMC is responsible(using the region map) for locating the RGM to carry out a givenrequest, for issuing the request to the selected RGM, and for retryingthe request if the selected RGM is unavailable (because, for example,the node has failed). In the latter case, a retry request will succeedwhen a new region map is received at the node.

As mentioned above, a region map identifies the node responsible foreach copy of each region. The virtual machine 412 (and each RGM, MM andMMC component therein) has access to the region map 405; a copy 420 ofthe region map, after it has been copied into the JVM, is also shown inFIG. 4. The region map thus is available to both the JVM and thedatabase in a given node. In this illustrative embodiment, each metadataobject has an attribute (e.g., a name), which is hashed to yield aninteger between 0x0 and 0x3fffffff inclusive, i.e., 30-bit values. Thesevalues can be represented comfortably in a signed 32-bit integer withoutrunning into overflow issues (e.g., when adding 1 to the high end of therange). The 30 bits allow for up to approximately 1 billion regions,which is sufficient even for large clusters. A region represents a setof hash values, and the set of all regions covers all possible hashvalues. There is a different bit position for each region, and thedifferent bit positions preferably are in a fixed order. Thus, eachregion is identified by a number, which preferably is derived byextracting the RegionLevelMap bits of the hash value. Where theconfiguration parameter is set to 6, allowing for 64 regions, theresulting hash values are the numbers 0x0 through 0x3f.

As previously noted, a region copy is in one of three (3) states:“authoritative,” “backup” and “incomplete.” If the region copy isauthoritative, all requests to the region go to this copy, and there isone authoritative copy for each region. If the region copy is a backup,the copy receives backup requests (from an authoritative region managerprocess). A region copy is incomplete if metadata is being loaded butthe copy is not yet synchronized (typically, with respect to otherbackup copies). An incomplete region copy is not eligible for promotionto another state until synchronization is complete, at which point thecopy becomes a backup copy. Each region has one authoritative copy and agiven number (as set by the metadataTPOF configuration parameter) backupor incomplete copies.

A backup region copy is kept synchronized with the authoritative regioncopy by enforcing a given protocol (or “contract”) between anauthoritative region copy and its TPOF backup copies. This protocol isnow described.

By way of brief background, when an update request is received at anMMC, the MMC does a lookup on the local region map to find the locationof the authoritative region copy. The MMC sends the update request tothe RGM associated with the authoritative region copy, which thencommits it. The update is also sent (by the RGM associated with theauthoritative region copy) to the RGM of each of the TPOF backup copies.The authoritative RGM, however, in order to indicate success, need notwait for each RGM associated with a backup region copy to commit theupdate; rather, when an RGM associated with a backup region copyreceives the update, it immediately returns or tries to return (to theauthoritative RGM) an acknowledgement. This acknowledgement is issuedwhen the backup request is received and before it is executed. In thecase where no failures occur, once the authoritative RGM receives all ofthe acknowledgements, it notifies the MMC, which then returns a successto the caller. If, however, a given failure event occurs, the protocolensures that the impacted RGM (whether backup or authoritative) removesitself (and potentially the affected node) from service, and a newregion map is issued by the MM leader. Preferably, the RGM removesitself from service by bringing down the JVM although any convenienttechnique may be used. The new map specifies a replacement for the lostregion copy. In this manner, each backup region copy is a “hot standby”for the authoritative region copy and is thus eligible for promotion toauthoritative if and when needed (either because the authoritative RGMfails, for load balancing purposes, or the like).

There are several ways in which the update process can fail. Thus, forexample, the authoritative region manager (while waiting for theacknowledgement) may encounter an exception indicating that the backupmanager process has died or, the backup manager process may fail toprocess the update request locally even though it has issued theacknowledgement or, the backup region manager process while issuing theacknowledgement may encounter an exception indicating that theauthoritative region manager process has died, and so on. As notedabove, if a given backup RGM cannot process the update, it removesitself from service. Moreover, when either a backup RGM or theauthoritative RGM dies, a new region map is issued.

The metadata management system keeps copies of a region synchronized. Anupdate that is done to an object in the authoritative region copy isreplicated on the backup region copies. Once an update is committed bythe authoritative RGM, the same update is applied to all backup regioncopies. The metadata management system ensures that any such failure(whether at the node level, the region manager level or the like) causesreassignment of region copies on the failed node; thus, the integrity ofthe remaining region copies is guaranteed. If a node containing anauthoritative RGM fails, then the backup RGMs are either in sync (withor without a currently executing update), or they are out of sync onlyby the update that was interrupted. In the latter case, re-synchronizingis easy. Because backup regions are kept synchronized with authoritativeregions, a promotion (from backup to authoritative) is instantaneous.

A node failure is also likely to lose backup regions. A backup region isrestored by creating, on some other node, a new, incomplete region. Assoon as the incomplete region is created, it starts recording updatesand starts copying data from the authoritative region. When the copyingis complete, the accumulated updates are applied, resulting in anup-to-date backup. The new backup region then informs the MM leader thatit is up to date, which will cause the MM leader to send out a mapincluding the promotion of the region (from incomplete to backup).

It should be noted that there is no requirement that the number ofregions correspond to the number of nodes. More generally, the number ofregions is uncorrelated with the number of nodes in the array ofindependent nodes. Additional details of the metadata management can befound in U.S. Pat. No. 7,657,581.

III. Multiple User-Defined Metadata for Self-Describing Objects

The usage of content in object storage systems is centered aroundutilizing network protocols for creation, reading, updating, anddeleting objects. While many protocols can be used, this descriptionwill be centered around the HyperText Transmission Protocol (HTTP) and,more specifically, the architectural styled for distributed systemscalled Representational State Transfer (REST) common with many web-basedclient/server implementations and typical with cloud based storagesystems. Each object system includes a processor, a memory, and at leastone object each being associated with a plurality of named collectionsof user-defined metadata.

A search on the Internet will bring up many high-level and detaileddescriptions of what HTTP/REST consist of, but the description belowwill focus on specific implementation relevant to this invention.Fundamentally, a request consists of a Universal Resource Locator (URL),an operation type, and an optional payload. In the context of an objectstorage system, the URL identifies the object for which the requestedoperation should be performed. The operations performed on objectsinclude GET, PUT, HEAD (get system-metadata), POST (update), and DELETE.

FIG. 5 shows an example of the core construction of an object. Objectsin an object system can have three main parts: fixed-content data,system metadata, and annotations (i.e., user-defined or custommetadata). The fixed-content data may be an exact digital reproductionof data as it existed before it was stored. Once it is in the objectsystem, the data typically cannot be modified but might be appendable.The system metadata includes system-managed properties describing thedata, such as its size and creation date. The system metadata typicallyincludes policy settings, such as retention or DPL (data protectionlevel), that affect how internal processes interact with the object. Thefocus of this description will be on the annotations including metadataa user or application provides to further describe an object. Asmentioned above, it may be specified as XML and is typically used tomake an object self-describing.

FIG. 6 shows an example of an object having system metadata and multiplenamed collections of user-defined metadata herein referred to asannotations. FIG. 7 shows an example of an object having a plurality ofannotations and access control lists (ACLs). Previously, an objectconsisted of one unnamed custom-metadata section. This inventionprovides for multiple named collections or elements of user-defined orcustom metadata called annotations. Each named collection of themultiple named collections associated with an object is separatelyaddressable by a single request which includes an addressable unit ofthe object and qualifying language specifying the particular namedcollection. While each named collection is separately addressable, it isalso possible to have an implementation whereby multiple namedcollections can be accessed at a time by a request. For illustrationpurposes, the samples in the description will use freely availableopen-source command line tool to perform HTTP/REST requests called curl(Command-line Universal Resource Locator). This tool provides a verysimple mechanism to perform HTTP requests without utilizing a full webbrowser. The examples of annotations in FIG. 7 include Land UsageAnalysis, Water Table Variations, Population Density Distribution,Government Agency Listing, and Elevation Deviation Data. Each annotationcould be generated by a separate program that analyzed the object imageas shown. Another example of an annotation of an object is one thatlinks or associates the object to another object.

The object may include an object-level access control list (ACL). Inaddition, each annotation may include its own annotation-level ACL, sothat different annotations may have different ACLs that may be differentfrom the object-level ACL. The annotation-level ACL of an annotationspecifies which requester can have access to that annotation.

Once an object exists, the annotations can be added, updated, or deletedutilizing HTTP REST requests. This is performed by specifying, via acontroller or a processor of an object system or the like, a URL to theexisting object, requesting a PUT operation, and supplying the contentof the annotation. The request URL not only provides the object, butalso directs the object storage web server to perform the specifiedoperation on which named annotation. Then supplied with the curl commandis the annotation content to be used for the operation against theobject. The format of the annotation (XML, JSON, binary, etc.) is notdictated by the object storage system; however, for illustrationpurposes, the annotation content will be represented in XML format.Whether the operation is allowed could depend on the configuration orpolicies applied to the object storage system. For instance, the objectstorage may be in read-only mode, may have access restrictions based onuser credentials, may have policies not allowing updating existingcontent, etc. However, for the illustration of the invention, it will beassumed the configuration and policies will allow for free access toobjects and their annotations.

Annotation HTTP REST Operations

As previously mentioned, there are a few operations that can beperformed against objects and annotations: GET, PUT, DELETE, POST, andHEAD. How to use these operations will be described below.

The first operation creates/replaces an annotation of the object. Thisis performed by issuing an HTTP PUT operation directed at the existingobject and supplying the new annotation content. The following is anexample command line to add/replace an annotation named foobar with thecontent in the annotation.xml file to an existing object object.xxx:

curl -T annotation.xml“http://ns1.ten1.hcp.example.com/rest/object.xxx?type=custom-metadata&annotation=foobar”

The next operation retrieves an annotation. This is performed by issuingan HTTP GET operation directed at the existing object. The annotationcontent will be returned in the body of the HTTP GET request response.The following is an example command line to retrieve the annotationnamed foobar associated with the object.xxx object and display it to theconsole of the user:

curl “https://ns1.ten1.hcp.example.com/rest/object.xxx?type=custom-metadata&annotation=foobar”

To retrieve the details (i.e., properties) of a specific annotationwithout retrieving the annotation, the following HTTP HEAD request canbe performed against the object providing additional directives on theURL specification. The following is an example curl command to performdisplay details about the foobar annotation for the object.xxx object:

 curl -I “http://ns1.ten1.hcp.example.com/rest/object.xxx?type=custom-metadata&annotation=foobar”

The following is an example output from this command:

HTTP/1.1 200 OK Expires: Thu, 01 Jan 1970 00:00:00 GMTX-HCP-ServicedBySystem: hcp.example.com X-HCP-Time: 1348516584X-HCP-SoftwareVersion: 5.1 X-RequestId: BE4012AB68AF46B Content-Type:text/xml Content-Length: 136 X-HCP-Type: annotation X-HCP-Size: 136X-HCP-ChangeTimeMilliseconds: 1348511536000.00 X-HCP-ChangeTimeString:2012-09-24T14:32:16-0400 X-HCP-Hash: MD57701F57B64ADD508FB986868790CA4FE X-HCP-Acls: Public:READ

To retrieve a list of all annotations for a given object, another formof an HTTP request is performed. There are two mechanisms that can beutilized. The first is performing an HTTP HEAD or GET request againstthe object; the response will consist of a simple name/size list. Forfull information about the annotations, an HTTP GET request can beperformed against the object providing an alternative directive in theURL request and the specification of how to present the list. Thefollowing is an example command line to retrieve the list of allannotations associated with the object.xxx object and display it to theconsole of the user in XML format:

curl “https://ns1.ten1.hcp.example.com/rest/object.xxx?type=custom-metadata-info” -H “Accept: application/xml”

An example output of the listing of annotation would consist of the nameand relevant object storage metadata about the annotation is thefollowing:

<annotations>  <annotation>   <name>HDI</name>   <hash>MD53970858C9F1BE83ED9DC6E837BE1D292</hash>  <changeTimeMilliseconds>1348593706000.00</   changeTimeMilliseconds>  <changeTimeString>2012-09-25T13:21:46-   0400</changeTimeString>  <size>74</size>   <contentType>text/xml</contentType>  <acl>Public:READ</acl>  </annotation>  <annotation>  <name>myCustomMetadata</name>   <hash>MD5BE83ED9DC6E837BE1D29272721A9F14F</hash>  <changeTimeMilliseconds>1348603222000.00</   changeTimeMilliseconds>  <changeTimeString>2012-09-25T16:00:22-   0400</changeTimeString>  <size>174</size>   <contentType>text/xml</contentType>  <acl>JohnD:READ,WRITE</acl>  </annotation> </annotations>

Finally, to delete an annotation associated with an object, an HTTPDELETE request is performed. The following is an example command linefor removing the foobar annotation from the object.xxx object:

curl -X DELETE“http://ns1.ten1.hcp.example.com/rest/object.xxx?type=custom-metadata&annotation=foobar”

There are additional/advanced mechanisms for sending and receivingcontent from object storage systems that also apply to the core APImechanisms shown above. The following are a partial list of theadditional mechanisms:

1) Included in the system is an unnamed annotation and this is equal tothe prior products' single custom-metadata container. It is included forbackward compatibility and can be accessed using the same mechanismspreviously mentioned by omitting the “annotation” URL specification ofthe request.

2) Compression of annotations while transmitting over the networkconnection can be used.

3) Usage of a single HTTP PUT (write) and HTTP GET operations isprovided that allows for a single HTTP operation to be used towrite/read both the object fixed content as well as an annotation. Thisis called Whole I/O in the existing product and was expanded to allowfor annotations. These requests can be referred to as Whole I/O PUTrequest and Whole I/O GET request.

4) Extension to existing query interfaces is used to providesearch/indexing reporting to include annotation information.

5) The features mentioned above are not limited to the HTTP/REST APIdescribed above, but are also utilized in the Web-Based GUI interfacefor the product.

FIG. 8 shows an example of an apparatus for implementing the use ofmultiple annotations for an object. The apparatus 800 may be part of anobject system (810 shown in broken lines) where the objects (812 shownin broken lines) are stored, or part of a management computer separatefrom a system 820 for storing the objects 822, or part of a system in aredundant array of independent nodes as described above (see FIGS. 1-4),or the like. The apparatus 800 includes a processor or controller 802and a memory 804, and is operable to perform operations on theannotations (e.g., PUT, GET, HEAD, POST, DELETE, Whole I/O PUT, WholeI/O GET), including the creation or updating of the access control lists(ACLs) of the annotations.

Of course, the system configurations illustrated in FIGS. 1, 4, and 8are purely exemplary of systems including content platforms orreplicated object storage systems in which the present invention may beimplemented, and the invention is not limited to a particular hardwareconfiguration. The computers and storage systems implementing theinvention can also have known I/O devices (e.g., CD and DVD drives,floppy disk drives, hard drives, etc.) which can store and read themodules, programs and data structures used to implement theabove-described invention. These modules, programs and data structurescan be encoded on such computer-readable media. For example, the datastructures of the invention can be stored on computer-readable mediaindependently of one or more computer-readable media on which reside theprograms used in the invention. The components of the system can beinterconnected by any form or medium of digital data communication,e.g., a communication network. Examples of communication networksinclude local area networks, wide area networks, e.g., the Internet,wireless networks, storage area networks, and the like.

In the description, numerous details are set forth for purposes ofexplanation in order to provide a thorough understanding of the presentinvention. However, it will be apparent to one skilled in the art thatnot all of these specific details are required in order to practice thepresent invention. It is also noted that the invention may be describedas a process, which is usually depicted as a flowchart, a flow diagram,a structure diagram, or a block diagram. Although a flowchart maydescribe the operations as a sequential process, many of the operationscan be performed in parallel or concurrently. In addition, the order ofthe operations may be re-arranged.

As is known in the art, the operations described above can be performedby hardware, software, or some combination of software and hardware.Various aspects of embodiments of the invention may be implemented usingcircuits and logic devices (hardware), while other aspects may beimplemented using instructions stored on a machine-readable medium(software), which if executed by a processor, would cause the processorto perform a method to carry out embodiments of the invention.Furthermore, some embodiments of the invention may be performed solelyin hardware, whereas other embodiments may be performed solely insoftware. Moreover, the various functions described can be performed ina single unit, or can be spread across a number of components in anynumber of ways. When performed by software, the methods may be executedby a processor, such as a general purpose computer, based oninstructions stored on a computer-readable medium. If desired, theinstructions can be stored on the medium in a compressed and/orencrypted format.

From the foregoing, it will be apparent that the invention providesmethods, apparatuses and programs stored on computer readable media forassociating multiple named collections of user-defined metadata toobjects. Additionally, while specific embodiments have been illustratedand described in this specification, those of ordinary skill in the artappreciate that any arrangement that is calculated to achieve the samepurpose may be substituted for the specific embodiments disclosed. Thisdisclosure is intended to cover any and all adaptations or variations ofthe present invention, and it is to be understood that the terms used inthe following claims should not be construed to limit the invention tothe specific embodiments disclosed in the specification. Rather, thescope of the invention is to be determined entirely by the followingclaims, which are to be construed in accordance with the establisheddoctrines of claim interpretation, along with the full range ofequivalents to which such claims are entitled.

What is claimed is:
 1. A storage system comprising: a processor; and amemory storing at least one object; the at least one object includingcontent data, system metadata and a plurality of named collections ofuser-defined metadata including annotations; wherein the processor isconfigured to manage an object-level access control list for the atleast one object and a plurality of annotation-level access controllists for the plurality of named collections of user-defined metadata toenable them to be separately addressable by a request, wherein theplurality of annotation-level access control lists for the plurality ofnamed collections of user-defined metadata specifies permissible accessto the plurality of named collections and are separately addressable bydifferent users, and wherein the object-level access control listspecifies permissible access to the at least one object and which isdifferent from the plurality of annotation-level access control listsfor the plurality of named collections of user-defined metadataassociated with the at least one object.
 2. The storage system accordingto claim 1, wherein the request is one of: a PUT request to create orreplace a named collection of user-defined metadata; a GET request toretrieve a named collection of user-defined metadata; a HEAD request toretrieve details of a named collection of user-defined metadata; a POSTrequest to update a named collection of user-defined metadata; a DELETErequest to delete a named collection of user-defined metadata; a WholeI/O (Input/Output) PUT request to create or replace the content data ofthe at least one object and a named collection of user-defined metadataassociated with the at least one object; or a Whole I/O GET request toretrieve the content data of the at least one object and a namedcollection of user-defined metadata associated with the at least oneobject.
 3. The storage system according to claim 1, further comprising:an unnamed collection of user-defined metadata which is addressable by arequest.
 4. The storage system according to claim 1, wherein theannotations included in the user-defined metadata for the at least oneobject include annotations in at least two different formats.
 5. In astorage system having a plurality of nodes, the nodes being grouped intoa plurality of cluster systems each having multiple nodes, each nodehaving a processor and a memory storing at least one object, the atleast one object including content data, system metadata and a pluralityof named collections of user-defined metadata including annotations, amethod of providing the user-defined metadata for the at least oneobject, the method comprising, for the at least one object: managing anobject-level access control list for the at least one object; andmanaging a plurality of annotation-level access control lists for theplurality of named collections of user-defined metadata to enable themto be separately addressable by a request, wherein the plurality ofannotation-level access control lists for the plurality of namedcollections of user-defined metadata specifies permissible access to theplurality of named collections and are separately addressable bydifferent users, and wherein the object-level access control listspecifies permissible access to the at least one object and which isdifferent from the plurality of annotation-level access control listsfor the plurality of named collections of user-defined metadataassociated with the at least one object.
 6. The method according toclaim 5, wherein the request is one of: a PUT request to create orreplace a named collection of user-defined metadata; a GET request toretrieve a named collection of user-defined metadata; a HEAD request toretrieve details of a named collection of user-defined metadata; a POSTrequest to update a named collection of user-defined metadata; a DELETErequest to delete a named collection of user-defined metadata; a WholeI/O (Input/Output) PUT request to create or replace the content data ofthe at least one object and a named collection of user-defined metadataassociated with the at least one object; or a Whole I/O GET request toretrieve the content data of the at least one object and a namedcollection of user-defined metadata associated with the at least oneobject.
 7. The method according to claim 5, further comprising:providing an unnamed collection of user-defined metadata which isaddressable by a request; and associating the unnamed collection ofuser-defined metadata with the at least one object.
 8. The methodaccording to claim 4, wherein the annotations included in theuser-defined metadata for the at least one object include annotations inat least two different formats.
 9. In a storage system having aplurality of nodes, the nodes being grouped into a plurality of clustersystems each having multiple nodes an apparatus comprising: acontroller; and a memory storing at least one object, the at least oneobject including content data, system metadata and a plurality of namedcollections of user-defined metadata including annotations; thecontroller being operable, for the at least one object, to: manage anobject-level access control list for the at least one object; and managea plurality of annotation-level access control lists for the pluralityof named collections of user-defined metadata to enable them to beseparately addressable by a request, wherein the plurality ofannotation-level access control lists for the plurality of namedcollections of user-defined metadata specifies permissible access to theplurality of named collections and are separately addressable bydifferent users, and wherein the object-level access control listspecifies permissible access to the at least one object and which isdifferent from the plurality of annotation-level access control listsfor the plurality of named collections of user-defined metadataassociated with the at least one object.
 10. The apparatus according toclaim 9, wherein the request is one of: a PUT request to create orreplace a named collection of user-defined metadata; a GET request toretrieve a named collection of user-defined metadata; a HEAD request toretrieve details of a named collection of user-defined metadata; a POSTrequest to update a named collection of user-defined metadata; a DELETErequest to delete a named collection of user-defined metadata; a WholeI/O (Input/Output) PUT request to create or replace the content data ofthe at least one object and a named collection of user-defined metadataassociated with the at least one object; or a Whole I/O GET request toretrieve the content data of the at least one object and a namedcollection of user-defined metadata associated with the at least oneobject.
 11. The apparatus according to claim 9, wherein the controlleris operable to: provide an unnamed collection of user-defined metadatawhich is addressable by a request; and associate the unnamed collectionof user-defined metadata with the at least one object.
 12. The apparatusaccording to claim 9, wherein the annotations included in theuser-defined metadata for the at least one object include annotations inat least two different formats.